Colorectal cancer (CRC) is the 3rd leading cause of cancer-related death in the United States. With the current standard of care, ~50% of patients will experience recurrence and death, highlighting the importance of developing preventative CRC therapies. In the context of this unmet clinical need for more effective CRC therapies, the previous discovery of a novel tumor suppressor which regulates epithelial integrity offers a unique opportunity to advance treatment and prevention for this disease. The transmembrane receptor guanylate cyclase C (GUCY2C) is well characterized as a key regulator of intestinal homeostasis upon in the APC/??-catenin activation by its paracrine hormone guanylin, the most commonly lost gene product in sporadic CRC. target ?? -catenin Preliminary studies revealed that suppression of guanylin occurs early on in the adenoma-carcinoma development of CRC. These mutations lead to stabilization and accumulation of ??-catenin in the nucleus which continuum, aligning with mutations pathway. Indeed, activation of the Wnt signaling drives epithelial dysfunction through increased TCF/LEF transcriptional activity. While APC and ?? -catenin pathway by mutations in APC (80%) or its downstream (15%) is a critical event in the APC/??-catenin-mediated suppression of mutations are well-defined primary transforming events in CRC, mechanisms leading from mutation to tumorigenesis remain elusive. We hypothesize that CRC arises from a state of hormone insufficiency, initiated elucidate mechanisms by which GUCY2C signaling reversibly regulates APC/??-catenin-driven tumorigenesis, by mutant guanylin in the colorectum, subsequently silencing the GUCY2C tumor suppressor, leading to tumorigenesis. The ultimate, long-term goal of this project is to signaling to the regulation of oncogenic ??-catenin. Leveraging unique mouse models of CRC and intestinal to inform the utility of GUCY2C ligand therapy in the prevention of CRC. To achieve this long-term objective, enteroid culture, we will define the mechanisms by which GUCY2C attenuates oncogenic ??-catenin. These two specific aims are proposed. In Aim 1, we will define the molecular mechanism linking GUCY2C results will establish GUCY2C as a critical mediator of epithelial transformation which can be targeted to overcome irreversible mutations that underlie the development of >90% of CRC. In Aim 2, we will define CRC activating mutations in ??-catenin to explore the utility of GUCY2C ligand replacement to prevent tumorigenesis, as a disease of hormone insufficiency that can be overcome by hormone replacement therapy. Using tissue-specific conditional mouse models developed in our laboratory, we will induce bi-allelic APC loss or to mitigate the risk of colorectal cancer in patients harboring APC/??-catenin mutations can be appreciated in informing a chemopreventive strategy to prevent CRC. The potential for immediate translation of these results the context of the recent FDA-approval of the oral GUCY2C ligands, linaclotide (Linzess?) and plecanatide (Trulance?), to treat chronic constipation syndromes.